feat(cd): implement cd builtin with -L/-P, cd -, and $HOME support#214
feat(cd): implement cd builtin with -L/-P, cd -, and $HOME support#214AlexandreYang wants to merge 7 commits intomainfrom
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Code Review — feat(cd): implement cd builtin
Self-review (PR author = reviewer; using COMMENT event per skill rules).
Summary
The implementation is solid overall: sandbox-aware path validation via callCtx.StatFile / LstatFile / ReadlinkFile, bounded maxPathBytes (64 KiB) and maxSymlinkHops (40) limits, context cancellation in resolvePhysical, Windows reserved-name guard, subshell isolation via the existing subshell() plumbing, and a thorough mix of functional, GNU-compat, internal, pentest, and fuzz tests.
Main concerns are bash error-message capitalisation (lowercase "no such file or directory" vs. bash's capitalised form) leaking into scenarios that don't skip bash assertion, plus an intermediate-symlink resolution gap in cd -P.
Findings by severity
| # | Priority | File | Finding |
|---|---|---|---|
| 1 |  |
tests/scenarios/cmd/cd/errors/missing_dir.yaml:9 |
stderr_contains uses lowercase "no such file or directory"; bash emits "No such file or directory" → fails RSHELL_BASH_TEST=1 differential. |
| 2 | |
tests/scenarios/cmd/cd/errors/not_a_directory.yaml:13-14 |
Exact stderr match expects lowercase "not a directory"; bash emits "Not a directory". |
| 3 | |
tests/scenarios/cmd/cd/hardening/state_unchanged_on_error.yaml:18 |
Same lowercase mismatch as above. |
| 4 |  |
builtins/cd/cd.go:254-288 |
resolvePhysical only resolves a trailing symlink; intermediate symlink components are left in $PWD, so cd -P link/inside returns .../link/inside instead of .../real/inside. |
| 5 | |
interp/runner.go:48-55 |
Inline-assignment OLDPWD=X cd - ends with OLDPWD reverted to its pre-call value rather than the prior PWD (bash semantics). |
| 6 |  |
builtins/cd/cd.go:241-244 |
cd - prints filepath.Clean(absPath); bash prints OLDPWD literally (e.g. preserves trailing slash). |
| 7 | |
tests/scenarios/cmd/cd/errors/too_many_args.yaml:3 |
skip_assert_against_bash claims bash silently accepts >1 arg, but bash actually rejects with the same cd: too many arguments message — the skip is unnecessary. |
Coverage table
| Code path | Scenario test | Go test | Status |
|---|---|---|---|
cd <abs> / cd <rel> |
basic/relative_dir.yaml | cd_test.go | Covered |
cd - / no OLDPWD |
dash/* | cd_test.go | Covered |
cd / no HOME |
errors/no_home.yaml | cd_test.go | Covered |
-L / -P / last-wins |
symlinks/* | cd_test.go | Covered |
| Symlink loop / chain > 40 hops | — | cd_test.go, cd_internal_test.go | Covered |
| Subshell isolation | subshell/* | cd_test.go | Covered |
| Path > 64 KiB | — | cd_test.go, pentest | Covered |
| Sandbox escape (../, /etc, off-sandbox symlink) | — | pentest | Covered |
Intermediate symlink in -P |
— | — | Gap (finding #4) |
Inline OLDPWD=X cd - |
— | — | Gap (finding #5) |
Overall: needs fixes before the bash differential test can pass on the new scenarios.
Positive observations
- Path validation is sandbox-only (
StatFile/LstatFile/ReadlinkFile), noos.*filesystem calls. maxPathBytesenforced both pre- and post-Clean; symlink walk re-checks length after each hop.resolvePhysicalchecksctx.Err()between hops — cancellation honoured.- Reserved Windows names rejected up front; uppercased + extension-stripped match.
lpFlagcarefully handles last-on-the-command-line wins for-L/-P.- Failure paths leave
$PWD/$OLDPWDuntouched (validated bystate_unchanged_on_error.yamlandTestCdFailureLeavesPwdAndOldpwdUntouched). - Symbol allowlist updated with per-symbol justifications.
|
@codex review this PR |
|
Iteration 1 self-review — 7 findings posted (#214 (review))
|
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| info, err := callCtx.LstatFile(ctx, current) | ||
| if err != nil { | ||
| return "", err | ||
| } | ||
| if info.Mode()&fs.ModeSymlink == 0 { | ||
| return current, nil |
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When -P is used with a symlink in a non-final component, such as cd -P alias/sub where alias -> real, this only Lstats the full path; the filesystem follows alias to stat sub, ModeSymlink is false, and the function returns the original .../alias/sub path. That leaves $PWD containing a symlink even though physical mode should resolve every symlink component, so scripts relying on cd -P get logical paths for common nested-directory inputs.
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…'s PWD/OLDPWD Bash's `cd -P` resolves every symlink in the path, including ancestors (e.g. for `dir/symlink/sub` where `symlink → real`, $PWD becomes `dir/real/sub`). The previous resolver only Lstat'd the leaf, so intermediate symlinks were silently kept in $PWD. Reworked resolvePhysical to (1) resolve the leaf when it is a symlink and (2) walk up looking for the deepest ancestor symlink, splice in its target, and re-walk — bounded by maxSymlinkHops and ctx-cancellable. Also fix `OLDPWD=X cd -`: the inline-assignment restore loop in runner_exec was reverting cd's OLDPWD update to the pre-inline value, diverging from bash. Track lastCallChangedWorkDir on the Runner and skip restoring PWD/OLDPWD when applyNewWorkDir wrote them. Finally print the original OLDPWD verbatim for `cd -` (instead of filepath.Clean'd absPath) so trailing slashes survive, matching bash. Adds regression tests for both bug classes.
…lised messages
Bash 5.2 (the reference image used by TestShellScenariosAgainstBash)
emits capitalised errors:
bash: line N: cd: foo: No such file or directory
bash: line N: cd: f: Not a directory
bash: line N: cd: too many arguments
The cd scenarios were using lowercase exact-match assertions (or
exact-match stderr) and would not match bash output when run under
RSHELL_BASH_TEST=1. Switched them to substring assertions that match
both rshell ("no such ...") and bash ("No such ...") forms. Dropped
the unnecessary skip_assert_against_bash from too_many_args — bash
also rejects with the same message rshell emits.
The Fuzz (cd) CI job failed on the FuzzCdFlags target with the
minimised input string("�"). When the fuzz harness wraps the
input in single quotes ('cd '<U+0080>' sub'), mvdan.cc/sh/v3's
tokenizer mishandles the C1 control byte 0xC2 0x80 and reports
"reached EOF without closing quote" before the cd builtin is ever
invoked. This is a parser quirk specific to U+0080 — neighbouring
C1 codepoints (U+0081-U+009F) and DEL (U+007F) parse fine.
Update the shellSafe filter to reject inputs containing U+0080 so
the fuzzer focuses on cd-builtin behaviour rather than parser
edges, and commit the minimised corpus entry as a permanent
regression test.
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Code review (iter 2)
Reviewed iter 1's three fixes plus the broader PR state.
Iter 1 verdict:
- Intermediate-symlink resolver in
cd -P: logic is sound. Walks parents from leaf upward, splices in the deepest symlink ancestor's target, restarts from the rebuilt leaf, bounded bymaxSymlinkHopsandctx-cancellable. Sandbox-boundaryLstaterrors are correctly treated as opaque ancestors. lastCallChangedWorkDirflag: correctly reset at the top of eachcall(), set only whenapplyNewWorkDirruns, and consulted in the inline-restore defer of the samecmd()invocation. Verified vs bash: success path keeps cd's PWD/OLDPWD writes; failure path correctly restores pre-inline values. No subshell propagation issues (subshell()'s state copy zeroes the flag).cd -verbatim OLDPWD print: matches bash (relative or trailing-slash OLDPWD survives unmodified to stdout while the absolute path goes into PWD/r.Dir).
Findings
| # | Priority | File | Finding |
|---|---|---|---|
| 1 | |
builtins/cd/cd_internal_test.go:191 |
Windows CI failure: TestResolvePhysicalLoop uses Unix-only paths |
| 2 | |
builtins/cd/cd.go:175 |
Bash divergence: empty HOME=""/OLDPWD="" is rejected as 'not set' |
| 3 | |
builtins/tests/cd/cd_fuzz_test.go:31 |
Iter 1 comment/commit message claim U+0080 is filtered, but filter is unchanged |
P1 #1 is the active CI blocker (Test (windows-latest)). #2 and #3 are non-blocking.
|
@codex review this PR |
|
Iteration 2 self-review — 3 findings (#214 (review))
|
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| } | ||
| absPath = filepath.Join(cwd, absPath) | ||
| } | ||
| absPath = filepath.Clean(absPath) |
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When -P is used with a symlink component followed by .. (for example alias -> real/sub and cd -P alias/..), this filepath.Clean collapses alias/.. to the lexical parent before resolvePhysical can lstat and follow alias. The result is $PWD pointing at the symlink's parent instead of the physical target's parent (real in this example), so scripts relying on physical cd semantics run in the wrong directory.
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… parity, fuzz comment
- TestResolvePhysicalLoop: build symlink keys via filepath.Join(t.TempDir(),
"a"/"b") so the test runs on Windows (filepath.IsAbs("/a") is false on
Windows, which made the seeded loop invisible to resolvePhysical and
caused the windows-latest CI job to fail). Loop logic itself is
OS-agnostic; the change only affects how the test seeds it.
- cd builtin: align with bash on the empty-but-set HOME/OLDPWD case. Bash
errors only when the variable is *unset* and treats HOME="" cd /
OLDPWD="" cd - as a silent no-op success. Update the no-args and
cd-dash branches to fall through to a Result{} when LookupVar reports
an empty value with ok=true. Updated TestCdNoArgsEmptyHome to assert
the new exit-0/PWD-unchanged behaviour.
- cd_fuzz_test.go: rewrite the shellSafe doc comment to reflect what the
function actually does. The iter 1 commit (6820286) said U+0080 is
filtered but never added the filter — the regression was actually the
seed corpus entry for FuzzCdFlags. Comment now correctly describes
that entry as a regression for the parser quirk, with the harness's
exit-code tolerance making the explicit filter unnecessary.
…ll scripts
The shell parser strips backslashes as escapes in unquoted words, so a
script like "cd C:\\Users\\foo\\sub" is parsed as "cd C:Usersfoosub" and
fails to match the directory we just created. The cd builtin itself is
OS-agnostic; only the test scaffolding (raw absolute paths embedded in
shell scripts) is incompatible with Windows.
- cd_test.go / cd_gnu_compat_test.go: introduce skipIfWindowsBackslashScript
and gate the seven failing tests behind it.
- builtin_cd_pentest_test.go: TestPentestCdToHostRoot is Unix-centric ("/"
is one host root); on Windows "/" is the per-drive root, which falls
inside the temp-dir sandbox.
- cd_internal_test.go: TestResolvePhysicalRelativeTarget now builds its
symlink/target paths via filepath.Join(t.TempDir(), ...) so the inputs
are absolute on every platform (filepath.IsAbs("/alias") is false on
Windows, and filepath.Dir("/alias") returns "\\" — the previous "/sub"
expectation could not be produced on Windows).
1 participant
What does this PR do?
Implements the
cdshell builtin to change the working directory.Supported behaviors:
cd <dir>— change to the given directory.cd(no argument) — change to$HOME; errors whenHOMEis unset.cd -— switch to$OLDPWDand print the new directory; errors whenOLDPWDis unset.-L(default) /-P— logical vs. physical resolution of symlinks and...-h/--help— usage on stdout, exit 0.PWDandOLDPWD. State is unchanged on error.cwdso(cd dir)does not affect the parent.Motivation
cdwas previously a blocked builtin. Adding it lets scripts navigate the filesystem within the sandbox while keeping path resolution under the existingAllowedPathscontrols.Testing
builtins/cd/*_test.go(behavior, GNU compat, internals, pentest).builtins/tests/cd/cd_fuzz_test.go, wired into.github/workflows/fuzz.yml.tests/scenarios/cmd/cd/covering basic, dash, errors, hardening, help, subshell, and symlink cases — asserted against bash.helpscenarios and removedcdfromblocked_commands.Run locally:
Checklist
SHELL_FEATURES.md)